Structure for increasing the loadcarrying capacity of a beam



Sheet c. KANDALL INVENTOR: CHA/nfs KANU/:LL

STRUCTURE FOR INCREASING THE LOAD-CARRYING CAPACITY OF' A BEAM Feb. 18,1969 Filed June 6, 19646 90A Rw ATTORNEY.

c. KANDALL 3,427,773 STRUCTURE FOR INCREASING THE LOAD-CARRYING CAPACITYOF A BEAM Feb. 18, 1969 Sheet Filed June 6, 1966 INVENTOR.'

CHARLES KANDALL ATTORNEY.

United States Patent O 3,427,773 STRUCTURE FOR INCREASING THE LOAD-CARRYING CAPACITY OF A BEAM Charles Kandall, 2383 Cornaga Ave., FarRockaway, N.Y. --11691 Filed June 6, 1966, Ser. No. 555,490 U.S. Cl.52-225 Int. Cl. E04c 3/10, 5/08 4 Claims ABSTRACT OF THE DISCLOSURE Mypresent invention relates to an improved method of increasing theload-carrying capacity of structural members, such as beams and girders,and structures embodying this method; more particularly, thisimprovement relates to the modification of the load-carrying capacity ofpre-existing structural members including beams or girders in placewithin existing structures and similar structural elements which havebeen designed on the basis of certain load-carrying characteristics butwhich require modification because of design changes, the desire toeliminate deflections and stress due to sustained loads and the like.

In structures such as buildings, bridges, elevated roadways and thelike, girders and beams frequently are provided to support a loadbetween spaced-apart locations spanned by these structural members andare designed to sustain the loads originally expected or predicted.Typical of such structures are 'beam and girder arrangements carryinga-iloor of concrete `or other structural material.

It frequently happens that the beams or girders must be altered so as toenable them to sustain loads greater than those for which they wereoriginally designed, or to distribute the loads differently from theoriginal system. The conventional method of effecting such increase inthe load-carrying capacity involves an increase in the section modulusof the girder or beam by riveting, bolting or welding steel plates,angles and other structural shapes to the top and bottom flanges of thestructural member. In cases in which the load is supported directlyabove the upper flange, such methods require the demolition, removal orlifting of the loading structure, while in some cases the existence ofsufficient headroom permits attachment, albeit with considerabledifficulty, of an appropriate structural shape to the bottom flange.Thus, it is frequently required to demolish a portion of an existingfloor to apply the requisite structural shape or shapes to the upperflange. Furthermore, since the beam or girder is supporting the load ithas Ibeen deformed and stressed thereby, and it is frequently necessaryto jack the beams up at one or more locations to relieve them of thedeadload stresses before the new steel shape is connected to the upperor lower flange. Any portions of the structure removed to afford accessto the beam or girder must then rbe repaired at substantial cost.

The general object of my present invention, therefore, is to provide amethod of and means for increasing the load-carrying capacity of a beam,girder or other loadbearing structural member without having to increaseits section modulus and, therefore, without the need for affix-3,427,773 Patented Feb. 18, 1969 ing structural shapes along the flangesof the structural member.

A further object of this invention is to provide a method ofredistributing the loading of a girder or beam which `avoids the needfor demolition and temporary removal of overlying structures and alsoany necessity for jacking the beam or girder to relieve dead-loadstress.

A further object of this invention is to provide a method of eliminatingthe deflection and stresses in an existing beam, lwithout the necessityof vertical jacking.

I have found, in accordance with the :present invention, that theaforestated objects can be realized by tensioning an elongated flexibletension element (a tendon) of polygonal configuration and anchoring it-to a compression member, specially provided for this purpose, which isfree and independent of the beam at the time of tensioning. Thepolygonal configuration is obtained by means of pins, brackets,stiffener plates or similar devices connected to the beam at locationsintermediate the anchoring locations and capable of taking the verticalcomponents of the tension. Thus, it s an important lfeature of thisinvention -that in the case of a generally horizontal beam adapted tosupport downward forces, including the dead weight of the Ibeam, thetendon or tension element is affixed thereto at a vertex of its polygonso as to produce an upward force by virtue of the tension applied tothat element. In this manner the dead loads, which cause bendingstresses in the girder, can be balanced in whole or in part bycounter-forces imparted to the structural member by the elongated orlongitudinally extending flexible tension element. As the dead loads arecounteracted by the upward vertical components of the tensioning steel,new additional dead or live loa-ds may be :placed on the member withoutthe necessity o-f increasing the section modulus. In accordance with animportant feature of this invention, this relieving of the stresses ofthe structural member is effected without applying additional stressthereto by installing an independent compression member-longitudinallyextending along the beam or girder and supported at the aforementionedforce-transfer locations-t0l anchor the wires, strands, cables or otherelements making up the tendon. The compression member is mounted `withfreedom of longitudinal displacement relative to the beam or girder toprevent direct axial (i.e., compressive) stress from being transferredto the girder.

Thus, if a simply supported girder having a tension element stretchedbetween force-transfer points at the extremities of the girder and atleast one vertex at which the tension element bears upon the girderbetween these points, an upward force is generated at any such vertex tocounteract the downward dead load or reduce the net downward loading ofthe girder at this point by any predetermined amount (as established bythe tension upon the element and the angle of attack at the vertex).Downward forces are applied a-t the anchor points corresponding to theforce-transfer locations mentioned earlier.

Once the cable or other tendon has been tensioned against thecompression member between the vertices at its bearing points upon thegirder, the compression member may be fixedly secured to the beam sinceit will not thereafter impart any compressive stresses to the beam,except temporarily under live load.

The term beam as herein used is intended to er1- compass all rolledsections, built-up girders or composite girder-type constructionelements, and trusses whether made from metal or from other elasticmaterials, although steel beams and girders are primarily contemplated.With a truss structure, it will be evident that the members spanning theupper end lower chords are the equivalent of the beamweb for thepurposes of the present invention. These structural shapes can be putinto place within an existing structure, as indicated earlier,

and indeed the present invention has its greatest applicability insituations in which the girder is under stress and its load-carryingcapabilities must be modified to balance additional stresses orcompensate for heavier types of load than originally contemplated. Inaddition, the invention pertains to structural members which may beencased in concrete subsequent to application of the tension element andcompression member and to encased structural members to which thetension element can be attached along a ank thereof.

The invention will be described in greater detail with reference to theaccompanying drawing in which:

FIG. 1 is a side-elevational view of a beam forming part of a structurewhose load-carrying capacity is to be increased in accordance with theprinciples of the invention;

FIG. 2 is an enlarged sectional view of an end portion of the bracingassembly of FIG.1;

FIGS. 3 and 4 are cross-sectional views taken on the lines III-III andIV-IV, respectively, of FIG. 1;

FIG. 5 is a side-elevational View similar to FIG. l, showing anotherembodiment;

FIG. 6 is a cross-sectional view taken on the line VI- VI of FIG. 5;

FIGS. 7, 8 and 9 are further views similar to FIG. 1 illustrating stillother modifications; and

FIG. 10 is a diagram illustrating the principles of the presentinvention in greater detail.

On referring first to FIG. 10, which illustrates an I- bea-m havingupper and lower flanges, it will be seen that the structural member issupported at S and S adjacent its extremities. If a load L is applied tothis beam, both the dead weight of the beam (represented by an arrow W)and the load L will bear downwardly and the downward forces will betransmitted to the supports S and S. If, in accordance with theprinciples of this invention, it is desired to balance all or part ofthe load applied to the beam in the region of the load L, a flexibletendon is stretched between force-transmitting points P' and P",preferably located directly above the supports S' and S for the directtransmission to these supports of the downward component of the forcesustained by the tension element T as represented by arrows F and F". Atits vertex V the tension element is anchored to the beam by meansdescribed in detail hereinafter and represented by a pin P. Since thetendon T is under high tension, an upward force component represented byarrow F will be applied to the beam to counteract the downward forcesthereon. The axial compression components C' and C of the tension wireare taken up by a compression member M specially provided for thispurpose, which is free and independent of the beam, and are thus nottransferred to the beam 1. The tension upon the tendon T is representedby the arrows T and T. The member M is slidable parallel to itself andis merely held against the beam to prevent buckling. To transmit thedownward forces F and F" to the support S' and S, I provide stitfenersto constitute force-transmitting members as described in detailhereinafter. These stifeners may be formed by the existing stiffeners ofconventional beams or plates or angles specially provided for thispurpose and such stiffening members can be reinforced in the regionsthrough which the tension element T passes.

From FIGS. l-4, it will be evident that the steel beam 1 rests upon apair of longitudinally spaced supports 11 and 12 and carries a dead loadrepresented by a concrete slab 10. The structure, of course, may alsoinclude additional beams, not shown, extending parallel to the beam 1.

The ybeam y1 is shown to lhave the usual `I-proiile with a lweb 13, anupper llange I14 and a lower flange 115. The flanges are spanned on oneor both sides of the web 13 by stitfener plates 16 ithrough which the`compression member can pass or upon which it may be mounted so that itsends are closer to ,said supports than to the midpoint of said member.The compression member 3, in this case, is a downwardly open angle, asbest seen in FIGS. 2 and 3 and is connected with the ends of a tensioncable or other tendon 2 by nuts and beveled washers 4 and 4 or othermeans conventionally used as anchors. Thus, when the cable 2 istensioned, axial compression forces are applied longitudinally to thecompression member 3. Such compression is not transferred to the beam 1since the compression member 3 is freely movable longitudinally of thebeam and only negligible friction forces are transmitted in longitudinaldirection therebetween. The tension element 2 and, of course, thecompression member Iaixed thereto are supported by brackets 5, orstiteners, similar to or identical with the stiffener plates 16 spanningthe llanges; the brackets 5 receive -tihe bar with freedom of relativesliding motion. Other brackets 6 with downwardly open recesses engagethe tendon 2 from above and serve to transmit the upward component ofthe forces of the cable to the beam 1 at the vertices of a polygoncorresponding ito intermediate p-oints between the bar-supporting frestsr16 and Athe anchor means represented generally at 4. The brackets 6represent any suitable means for transmitting the upward Kforce to thestructural member. 1As can 'be seen from fFIG. 4, cross beams 7interengaging with beam 1 may be provided with brackets `7' andapertured to guide the compression member 3 and the tension element 2.

In order to compens-ate for any weakening of the cross beams 7 or thestiffener -16 by the apertures requi-red for the passage of elements 21an-d 3, the lregion surrounding these apertures may be lreinforced withplates, Iangles or Ithe like. From FIG. 4 ilt can be seen that thecompression member 3 may be mounted along and youtwardly of Itheconnection angles y8 whereas bracket members 5 serve for lthis purposein the arrangement of FIIG. 3.

,The points of engagement between the cable 2 and the beam 1 'lie alonga polygonal line which can substantially coincide 'with the moment lineof the supported structure under dead load so that, as a consequence ofthe provision of the tensioning element 2, the load may be substantiallyuniformly distributed over the girder even though a nonuniform stressdistribution was originally present. Naturally, each of the other beamsof the structure, extending parallel to the beam 1, may be strengthenedin like manner with Ithe corresponding bracing assemblies 2, 3preferably Edisposed symmetrically on, Ifor example, confronting sidesof adjacent beams. In cases where cross beams do not exist, bracingassemblies may be mounted symmetrically on opposite sides of the web 13of a single beam.

Conventional means (e.g., hydraulic cylindrical arrangements) may beused for tensioning the cable 2 and anchoring the terminals to thecompression member 3 to retain the cable under sufficient tension tokeep the beam 1 substantially horizontal or even slightly camberedupwardly, under dead load, without subjecting this beam to anylongitudinal compression. The compression member 3 may remain free ofthe beamr after tensioning or may be connected by welding to the pointsat which it is supported; such attachment does not alter the fact thatthe axial stress is taken up by the compression member.

FIGS. 5 and 6 show a generally similar arrangement wherein the beam 1has been replaced by a built-up girder 1a with cover plates 18 and 19included in its upper and lower anges. Stiffeners 8a carry brackets 5a,6a through which the compression member 3a and the tension cable 2apass. The compression member 3a is here shown to have an H-profile. Itwill be apparent that, in this arrangement also, the force-transmittingsupport plates for the assembly 2a, 3a and the means for attaching thetension element 2a to the beam at the vertices of the polygon can beformed at least in part by transverse beam or brackets as shown in FIGS.1 and 4 or that elements 2a, 3a may pass directly through the stifeners,without requiring angles or the like to be mounted thereon as shown inthe left-hand side of FIG. 6.

In FIG. 7 I have shown a conventional continuous beam 1b resting on anintermediate support 20` in addition to the two end supports 11, 12. Thetension cable 2b again extends substantially along the moment line in apolygonal coniguration and bears upon the compression member 3b only atits extremities while being anchored at intermediate locations(corresponding to vertices of the polygon) to the |beam. IIn the systemof FIG. 8, the beam 1c overhangs the supports 11 and 12 while the cablepolygons likewise extend beyond these supports. In contradistinction tothe preceding embodiments the compression member 3c extends underneaththe associated tension cable 2c in this arrangement.

FIG. 9, nally, illustrates the possibility of subdividing a bracingassembly according to my invention into a plurality of tension elements2d, 2d', 2d with respective compression members 3d, 3d', 3d, all carriedon the web of the beam 1d; the smaller tension cables 2d', 2d" are oftriangular conguration with their apices overlying the supports 11, 12and lying close to the extremities of the main cable 2d. Thelongitudinal slidability and mounting of the compression members and themeans whereby the cables are anchored to the beam are essentially thesame as those described with reference to the previous embodiments.While nuts have been illustrated for convenience, other clamping devicesconventionally used to anchor the terminals of cables can be employed.

The invention described and illustrated hereinabove is considered toadmit of many modifications and variations which will be readilyapparent to those skilled in the art and are intended to be includedwithin the spirit and scope of the appended claims.

I claim:

1. A structure comprising a substantially horizontal beam resting on atleast two horizontally spaced supports; a compression-resistantelongated member extending alongside said beam and having ends atlocations closer to said supports than to the midpoint of said member;laterally extending means on said lbeam forming rests for the ends ofsaid member while leaving said ends free to move longitudinally withreference to said rests; a exible elongated tension element anchoredunder stress to the ends of said member and extending downwardly fromsaid ends; and laterally extending bracing means rigid with said beambearing downwardly upon at least'one intermediate point of said tensionelement whereby the latter exerts an upward thrust upon said lbeam atsaid intermediate point without subjecting said beam to longitudinalcompression.

2. A structure as defined in claim 1, further comprising retaining meansfor holding said member against said beam to prevent buckling of saidmember.

3. A structure as defined in claim 2 wherein said beam has a web, anupper flange and a lower flan-ge, said element and member extendingalong said web between said anges.

4. A structure as dened in claim 3 wherein said element is connectedwith said web at a plurality of intermediate locations Iby laterallyprojecting formations disposed substantially along the moment line ofthe structure.

References Cited UNITED STATES PATENTS 1,598,693 9/1926 Sereif 52-6942,510,958 6/1950 COff 52-225 2,786,349 3/1957 Coil 52-723 2,822,068 2/1958 Hendrix 52-226 3,010,257 11/1961 Naillon 52-225 3,140,764 7/ 1964Checkin 52-645 3,269,069 8/ 1966 Carlson 52-227 FRANK L. ABBOTT, PrimaryExaminer.

JAMES L. RIDGILL, JR., Assistant Examiner;

U.S. Cl. X.R.

